1. Field of the Invention
The present invention relates to a magneto-resistive element and a magnetic head for data writing/reading. The present invention also relates to a data writing/reading device which writes/reads data on/from a magnetic recording medium.
2. Description of the Related Art
A magnet-resistive element (or a magnetic head) has been known as an element which can read high density data recorded on a magnetic material.
As disclosed in, for example, a paper titled xe2x80x9cThin Film Magnetoresistors in Memory Storage and Related Applicationsxe2x80x9d written by D. A. Thompson (IEEE TRANSACTIONS ON MAGNETICS, MAG-11, no. 4, p. 1039; 1975), operation of the magneto-resistive element is based on AMR (anisotropic magnetoresistance) effect. According to the AMR effect, one component of resistance in the magneto-resistive element changes. The change degree is in proportion to a cosine (of an angle between the magnetization direction of the magneto-resistive element and the flow direction of a current in the magneto-resistive element) to the second power.
Bias magnetic field is applied to an AMR head (a magnetic head utilizing the AMR effect) in order to reduce Barkhausen noise. An antiferromagnetic material such as FeMn, NiMn, and nickel oxidew is a material which applies the bias magnetic field.
As another type of the magnetic head, a GMR (giant magnetoresistance) head which utilizing GMR effect (spin valve effect) has been known. The GMR head has a pair of ferromagnetic layers sandwiching a non-magnetic layer. According to the GMR effect, changes of resistance between the ferromagnetic layers changes. The change degree is in proportion to a cosine of an angle between the magnetization directions of the ferromagnetic layers. The GMR head is more sensitive than the AMR head. In other words, the degree of resistance changes in the GMR head caused by magnetic field is larger than that of the AMR head.
Various techniques for improving performance of the above described magnetic head (magnetic sensor) have been disclosed in Unexamined Japanese Patent Application KOKAI Publication Nos. H2-61572, H4-358310, and H4-103014, Japanese Patent No. 2701748, and the U.S. Pat. No. 5,390,061.
According to the technique disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H2-61572, the magnetization directions of a pair of the ferromagnetic layers sandwiching a non-magnetic layer are controlled in order to improve sensitivity of the magnetic head. More precisely, the magnetization direction of one ferromagnetic layer and another magnetization direction of the other ferromagnetic layer are controlled so as to be parallel or anti-parallel in accordance with external magnetic field.
According to the technique disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H4-358310, the magnetization directions of ferromagnetic films which are separated by a non-magnetic film are controlled in order to improve sensitivity of the magnetic head. More precisely, the magnetization direction of one ferromagnetic film and another magnetization direction of the other ferromagnetic film are controlled so as to be perpendicular to each other when no external magnetic field is applied thereto.
According to the technique disclosed in Japanese Patent No. 2701748, bias magnetic field is applied to the magnetic head in order to improve sensitivity of the magnetic head. More precisely, the disclosed magnetic head has two magnetic films, each having different coercive force, which are deposited while sandwiching a non-magnetic layer therebetween. In this technique, the direction of the applied bias magnetic field is the same as the direction of remained magnetization of the magnetic film having larger coercive force.
In a magnetic sensor disclosed in Unexamined Japanese Patent Application KOKAI Publication No. H4-103014, the magnetization directions of magnetic layers sandwiching a non-magnetic layer are controlled by applying bias magnetic field thereto in order to improve sensitivity of the magnetic sensor. More precisely, the applied bias magnetic field controls the magnetization direction of one magnetic layer and another magnetization direction of the other magnetic layer so as to be parallel or anti-parallel.
According to the technique disclosed in U.S. Pat. No. 5,390,061, positional relationship between magnetic layers and a recording surface of a magnetic recording medium is controlled in order to read data from the high density recording medium. More precisely, the magnetic layers are formed on a Cu or AL electrode so that surfaces of the magnetic layers are perpendicular to the recording surface of the magnetic recording medium. Thus, a region of the magnetic sensor which contacts the recording surface is reduced.
In order to improve performance of the magnetic sensor, other than the above techniques, a non-magnetic layer to be formed on an electrode should be flattened, and the electrode should be strongly affixed to layers sandwiching the electrode.
FIG. 22 shows uneven thickness of a non-magnetic layer. That is, unflat non-magnetic layer is likely to cause current leakage which will reduce sensitivity of the magnetic sensor. Moreover, a current through the non-magnetic layer is likely to break thin portions of the non-magnetic layer. In other words, the unflat non-magnetic layer worsens withstand voltage characteristics of the magnetic sensor (magneto-resistive element).
If bond strength of the electrode is not strong, the electrode is exfoliated easily from the layers which sandwich the electrode. Such the magnetic sensor (magneto-resistive element) has poor reliability and yielding.
Further a data writing/reading device comprising the above magnetic sensor also has poor reliability.
None of the above described Thompson""s paper, Unexamined Japanese Patent Application KOKAI Publication Nos. H2-61572, H4-358310, and H4-103014, Japanese Patent No. 2701748, and U.S. Pat. No. 5,390,061 has descriptions regarding to a method for flattening a non-magnetic layer and bond strength of an electrode.
It is an object of the present invention to provide a magneto-resistive element having improved reliability. It is another object of the present invention to provide a magneto-resistive element having a flat magneto-resistive layer. It is a further object of the present invention to provide a magneto-resistive element which has an electrode having strong bond strength. It is still another object of the present invention to provide a magnetic head and a data writing/reading device having improved reliability.
According to this invention, the magneto-resistive layer is formed on an electrode which has an average surface roughness equal to or smaller than about 0.3 nm. Thus, current leakage, breaking of the non-magnetic layer, and the like do not occur. As a result, the magneto-resistive element has excellent reliability. A second electrode is formed on the magneto-resistive layer. The magneto-resistive layer may include a non-magnetic layer. In an embodiment, the magneto-resistive layer may include at least one magnetic layer along with the non-magnetic layer. The magneto-resistive layer in one embodiment may have a pair of magnetic layers sandwiching a non-magnetic layer.
According to this invention, the non-magnetic layer formed on the first electrode is flat because the average surface roughness of the first electrode is equal to or smaller than 0.3 nm. Thus, current leakage, breaking of the non-magnetic layer, and the like do not occur. As a result, the magneto-resistive element has excellent reliability.
The electrode may be made of a material which prevents it from being exfoliated from a layer formed directly thereon.
The electrode may be made of a material including at least one of Ta, Zr, Ti, Hf, W, Mo, Y, V, Nb, Au, Ag, Pd, and Pt. In this case, the electrode may be affixed to the magneto-resistive layer with bond strength of equal to or greater than 36 Giga Pascal (Gpa).
According to a second aspect of the present invention a magnetic head is formed with the above described magneto-resistive element.
A data writing/reading device may be formed using the aforementioned magnetic head.